(Citadel ign gazebo+Foxy) How to control a single joint using diff driver?

edit

I was learning how to use Foxy with Citadel. I noticed that this generates 4 topics in the launch

 # Bridge
bridge = Node(
    package='ros_ign_bridge',
    executable='parameter_bridge',
    arguments=['/model/vehicle_blue/cmd_vel@geometry_msgs/msg/Twist@ignition.msgs.Twist',
               '/model/vehicle_blue/odometry@nav_msgs/msg/Odometry@ignition.msgs.Odometry',
               '/model/vehicle_green/cmd_vel@geometry_msgs/msg/Twist@ignition.msgs.Twist',
               '/model/vehicle_green/odometry@nav_msgs/msg/Odometry@ignition.msgs.Odometry'],
    output='screen'
)

But then I decided to add double diff drivers like this in the robot model:

  <plugin
    filename="ignition-gazebo-diff-drive-system"
    name="ignition::gazebo::systems::DiffDrive">
    <left_joint>rear_left_wheel_joint</left_joint>
    <right_joint>rear_right_wheel_joint</right_joint>
    <wheel_separation>1.25</wheel_separation>
    <wheel_radius>0.3</wheel_radius>
  </plugin>

   <plugin
    filename="ignition-gazebo-diff-drive-system"
    name="ignition::gazebo::systems::DiffDrive">
    <left_joint>front_left_wheel_joint</left_joint>
    <right_joint>front_right_wheel_joint</right_joint>
    <wheel_separation>1.25</wheel_separation>
    <wheel_radius>0.3</wheel_radius>
  </plugin>

I don't see any specific joint. Let's say, I want to control the front right wheel only. How do I do that?

I wrote the simple code and it kinda focus on forward, left, right and backward. I can't find a way to control one joint only. Here is the code I wrote:

#!/usr/bin/env python3

import sys
import time

import geometry_msgs.msg
import rclpy

if sys.platform == 'win32':
    import msvcrt
else:
    import termios
    import tty


rclpy.init()
node = rclpy.create_node('teleop_twist_keyboard')
pub = node.create_publisher(geometry_msgs.msg.Twist, '/model/vehicle_green/cmd_vel', 10)

def backward():
    twist = geometry_msgs.msg.Twist()
    twist.linear.x = 2.0  # positive goes backward, negative goes forward
    twist.angular.z = 0.0
    print("Backward.")
    pub.publish(twist)
    time.sleep(0.5)
    twist.linear.x = 0.0
    twist.angular.z = 0.0
    pub.publish(twist)


if __name__ == '__main__':
    backward()

I tried to change from geometry_msgs.msg.Twist, '/model/vehicle_green/cmd_vel' to `geometry_msgs.msg.Twist, '/model/vehicle_green/front_left_wheel_joint/cmd_vel' and it didn't work. Do you have any suggestion?